Dynamic Stability and Mid Axial Preload Control for a Tie Shaft Coupled Axial High Pressure Rotor

ABSTRACT

A middle support member is used to provide axial support and control to the tie shaft. The middle support member includes a high pressure compressor coupling nut that applies a preload that allows the high pressure compressor stack to be installed separately from the high pressure turbine rotor through a kickstand.

BACKGROUND

This application relates to a method of assembling a gas turbine engine,wherein both a compressor rotors and the turbine rotors are assembledusing a tie shaft connection.

Gas turbine engines are known, and typically include a compressor, whichcompresses air and delivers it downstream into a combustion section. Theair is mixed with fuel in the combustion section and combusted. Productsof this combustion pass downstream over turbine rotors, driving theturbine rotors to rotate.

Typically, the compressor section is provided with a plurality of rotorserial stages, or rotor sections. Traditionally, these stages werejoined sequentially one to another into an inseparable assembly bywelding or separable assembly by bolting using bolt flanges, or otherstructure to receive the attachment bolts.

More recently, it has been proposed to eliminate the welded or boltedjoints with a single coupling which applies an axial force through thecompressor rotors stack to hold them together and create the frictionnecessary to transmit torque.

SUMMARY

A gas turbine engine has a compressor section carrying a plurality ofcompressor rotors and a turbine section carrying a plurality of turbinerotors. The compressor rotors and the turbine rotors are constrained torotate together with a tie shaft. An upstream hub provides an upstreamabutment face for the compressor rotors stack. A downstream hub boundsthe upstream end of the compressor rotor and abuts the compressor rotorstack against the upstream hub.

The downstream hub creates a middle support used to provide radialsupport for a high pressure rotor and control to the tie shaft preload.The middle support also includes a high pressure compressor coupling nutthat applies a preload that allows the high pressure compressor stack tobe installed separately from the high pressure turbine rotor. The middlesupport is essential to control the dynamic stability of the long highpressure rotor spanning the distance between its forward and aftsupports. The aft support includes a multiple layer interference fitbetween the shaft and the most downstream turbine rotor. The multi-layerfit accomplishes simultaneously radial support for the rotors stack anddynamic stability for the high pressure spool

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional perspective view of a turbine engineaccording to the claims;

FIG. 2 is an enlarged view of the engine with the middle support member;and

FIG. 3 is an enlarged view of the HP Rotor AFT end support memberaccording to the claims.

DESCRIPTION

FIG. 1 illustrates a turbofan gas turbine engine 10 of a type preferablyprovided for use in subsonic flight, generally including a fan 12through which ambient air is propelled, a multistage compressor 14 forpressurizing the air, a combustor 16 in which the compressed air ismixed with fuel and ignited for generating an annular stream of hotcombustion gases, and a turbine section 18 for extracting energy fromthe combustion gases. In the illustrated arrangement, by-pass air flowslongitudinally around the engine core through a by-pass duct 20 providedwithin the nacelle. The compressor 14 and turbine 18 may be connected ina variety of ways, such as through a shaft, through one or more tieshafts, through a transmission, etc.

Referring to FIG. 2, a long span between supporting bearings 350 and 330creates rotor dynamic problems for bearing preload and rotor stability.Bearings apart from being mounted on the shafts and housings have to bepreloaded properly for their proper functioning. Preloading is themethodology by which the internal clearance in the bearing is removed byapplying a permanent thrust load to it. In other terms, the bearing ispushed to such an extent that it has to move only in the groove(raceway) and cannot move axially in either direction. Preloading may beneeded for several reasons such as to eliminate the radial and axialplay in the bearing which would be inherently present even after abearing is mounted radially on a shaft, eliminate all the unnecessaryclearances, which may induce a rigidity to the bearings and thus to thesystem the bearing supports and by reducing the clearances, therotational accuracy of the bearing may be controlled. Thus, it helps toreduce the non-repetitive run out that could occur because of theclearances.

To address these requirements, it may be necessary to provide a support#3 between supports #1 and #2, and for the rotors 313 324 to retain atight radial fit with the tie shaft 322 at support locations throughoutthe mission envelope. Axial preload in the compressor and turbine rotorstacks 313 and 324 may be required to generate the friction betweenadjoining rotor faces for torque transmission. The downstream hub 341acts as a middle support member to address these requirements. Themiddle support member 341 may allow the compressor stack 313 to beassembled separately with a temporary preload applied by the HPCcoupling nut 332. It may be necessary for the coupling nut 332 axialinterface to retain a minimum axial preload throughout the missionenvelope to satisfy dynamic stability requirements and prevent anaxially loose nut from whirling.

FIG. 2 schematically illustrates a gas turbine engine 10 incorporating acombustion section 311, shown schematically, a compressor section 313having a plurality of compressor rotors 338, and a turbine section 324having a plurality of turbine rotors 325. As shown, an upstream hub 334may be threadably secured to the tie shaft 322 at the upstream side ofthe compressor section 313. A downstream hub/middle support member 341may be positioned at a downstream side of the compressor stack 313, andcontacting a downstream-most compressor rotor 315. The stack ofcompressor rotors 313 may be sandwiched between the downstream hub 341and upstream hub 334, and secured by a HPC lock nut 332. The downstreamhub/middle support member 341 may abut the stack of turbine rotors 324that are secured with the high pressure turbine (HPT) lock nut 327 (FIG.3). Lock Nut 401 may bias a plurality of seals and bearings against theturbine rotors. The two lock nuts 327 and 401 may be threadably engagedto the same tie shaft 322. The high pressure turbine coupling nut 327applies the primary preload to HPC stack 313 and HPT stack 324. As shownin FIG. 3, the nut 327 may be threadably received on threads 458 on thetie shaft 322. FIG. 3 illustrates the nuts 401 and 327 threadablyengaged to tie shaft 322. Initially, the upstream hub 334 (FIG. 2) maybe threadably assembled to the tie shaft 322 while the compressor rotors338 and 315 and downstream hub/middle support member 341 may be stackedtogether using lock nut 332 to secure all of them by applying a axialpreload force holding the rotors against the kickstand 343 of theupstream hub 334. An internal compression load may be created in therotors stack to react the tension load in the tie shaft 322.

The kickstand 343 of the downstream hub/middle support member 341 isdesigned as a soft spring to enable the secondary load path from the HPCCoupling Nut 332 through the kickstand 343, downstream hub/middlesupport member 341 and compressor rotors stack 313. The secondary loadpath may prevent rolling and may ensure self alignment with the matingface of the HPC coupling nut 332. The kickstand 343 of the arrangementmay also generate radial and axial reactions at the downstreamhub/middle support member 341 interface with the last compressor rotor315. The secondary load path applies a preload that is mostly temporaryas it decreases significantly after the HPT Nut 327 is tightened—theresidual secondary preload may also create loaded contact between thekickstand 343 of the downstream hub/middle support member 341 and theHPC coupling nut 332 even for conditions when the HPC coupling nut tendsto separate.

For the HP Rotor downstream end, the radial preload may be realizedthrough a multi-layered fit arrangement (Fits A 420, B 430 and C 440 inFIG. 3) between bearing 330, intermediary sleeve 465, HPT rotor arm 467and the tie shaft 322.

The turbine rotors 325 may be axially preloaded using lock nut 327 tosecure the new assembly by applying an axial preload force holding thecompressor 313 and turbine rotors 324 together and ensuring thenecessary friction to transmit torque. As soon as the HPT Nut 327 istightened, the primary load path is transferred from the kickstand 343to the cylindrical portion of the downstream hub/middle support member341 and HPT stack 324 with internal compression load in the compressorrotors stack and 313 and turbine rotors stack 324, and tension load inthe downstream end of the tie shaft 322.

The three fit 420 430 440 arrangement may ensure that the compressor andturbine sections are reliably held together, will be capable to resistthe forces to be encountered during use, transmit the necessary torqueand satisfy dynamic stability requirements. All these functions may beaccomplished within a minimal radial envelope and with a low-profilelocking ring 458

As a result of the arrangement, axial preload may be achieved with asingle fastener (tie shaft) 322. The preload may be distributed betweenthe primary path (backbone) and the secondary path (kickstand 343) in abalanced manner such that there is a minimum loss in clamping capabilitywhile the dynamic stability is maintained for a long-span, high speedrotor (>20,000 RPM). The multi-layer snap illustrated in FIG. 4accomplishes simultaneously radial support for the rotors stack, dynamicstability for the high pressure spool and a leak-proof joint for thesecondary air system.

Although embodiments of this invention have been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention. In accordance with the provisions of thepatent statutes and jurisprudence, exemplary configurations describedabove are considered to represent a preferred embodiment of theinvention. However, it should be noted that the invention can bepracticed otherwise than as specifically illustrated and describedwithout departing from its spirit or scope.

1. A high pressure spool of a turbine engine comprising: a first hub ona first end of a tie shaft; a second hub on a second end of the tieshaft; and a middle support member between the FWD and AFT ends of theHP Rotor wherein the middle support member further comprises: a highpressure compressor coupling nut which couples a kickstand incommunication with the HPC stack to the tie shaft; and An AFT supportcomprising: a high pressure turbine coupling nut; a lock ring; and amultiple layer interference fit between the shaft, the high pressureturbine disk and a bearing stack.
 2. The high pressure spool of aturbine engine of claim 1 wherein the kickstand of the middle supportmember provides a support between the FWD and AFT ends of the HP Rotorand accepts a secondary load.
 3. The high pressure spool of a turbineengine of claim 1, wherein the kickstand of the middle support memberprovides positive axial and radial reactions in the middle supportmember.
 4. The high pressure spool of a turbine engine of claim 1,wherein the high pressure compressor coupling nut applies a preload tothe compressor rotors stack.
 5. The high pressure spool of a turbineengine of claim 4, wherein the high pressure compressor nut allows thehigh pressure compressor stack to be installed separately from the highpressure turbine rotor.
 6. The high pressure spool of a turbine engineof claim 1, wherein the turbine end of the tie shaft comprises a turbinecoupling nut that applies a preload to the compressor and turbine rotorsstacks.
 7. The high pressure spool of a turbine engine of claim 1,further comprising a multi-layered fit arrangement for the HP Rotor AFTend which creates a radial preload.
 8. The high pressure spool of aturbine engine of claim 7, wherein the HP coupling nut is securedagainst unlocking by using the locking ring wherein the locking ring isa low-profile locking ring which provides a minimal radial envelope. 9.A turbine engine with a tie shaft and a HP rotor comprising: a fanrotatable about an axis, the fan including a plurality ofradially-extending fan blades a combustor which exhaust high speed airinto a turbine, the turbine comprising a HP rotor wherein the rotor isrotatable about an axis, an upstream hub on a first end of a tie shaft;and a middle HP rotor support member between the FWD and AFT ends of theHP Rotor wherein the middle support member further comprises: a highpressure compressor coupling nut which couples a kickstand incommunication with the HPC stack to the tie shaft; and An AFT HP rotorsupport comprising: a high pressure turbine coupling nut; a low profilelock ring; and a multiple layer interference fit between the shaft, thehigh pressure turbine disk and a bearing stack.
 10. The turbine engineof claim 9, wherein the kickstand of the middle support member providesa support between the FWD and AFT ends of the HP Rotor and accepts asecondary load.
 11. The turbine engine of claim 9, wherein the kickstandof the middle support member provides positive axial and radialreactions in the middle support member.
 12. The turbine engine of claim9, wherein the high pressure compressor coupling nut applies a preloadto the compressor rotors stack.
 13. The turbine engine of claim 12,wherein the high pressure compressor nut allows the high pressurecompressor stack to be installed separately from the high pressureturbine rotor.
 14. The turbine engine of claim 9, wherein the turbineend of the tie shaft comprises a turbine coupling nut that applies apreload to the compressor and turbine rotors stack.
 15. The turbineengine of claim 14, further comprising a multi-layered fit arrangementfor the HP Rotor AFT end which creates a radial preload.